package org.apache.solr.spelling;

import java.io.File;
import java.io.IOException;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import org.apache.lucene.analysis.Token;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.spell.Dictionary;
import org.apache.lucene.search.spell.LevensteinDistance;
import org.apache.lucene.search.spell.SpellChecker;
import org.apache.lucene.search.spell.StringDistance;
import org.apache.lucene.search.spell.SuggestWord;
import org.apache.lucene.search.spell.SuggestWordFrequencyComparator;
import org.apache.lucene.search.spell.SuggestWordQueue;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.store.RAMDirectory;
import org.apache.solr.common.util.NamedList;
import org.apache.solr.core.SolrCore;
import org.apache.solr.search.SolrIndexSearcher;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * Abstract base class for all Lucene-based spell checking implementations.
 * 
 * <p>
 * Refer to <a href="http://wiki.apache.org/solr/SpellCheckComponent">SpellCheckComponent</a>
 * for more details.
 * </p>
 * 
 * @since solr 1.3
 */
public abstract class AbstractLuceneSpellChecker extends SolrSpellChecker {

    public static final Logger log = LoggerFactory.getLogger(AbstractLuceneSpellChecker.class);
    public static final String SPELLCHECKER_ARG_NAME = "spellchecker";
    public static final String LOCATION = "sourceLocation";
    public static final String INDEX_DIR = "spellcheckIndexDir";
    public static final String ACCURACY = "accuracy";
    public static final String STRING_DISTANCE = "distanceMeasure";
    public static final String COMPARATOR_CLASS = "comparatorClass";
    public static final String SCORE_COMP = "score";
    public static final String FREQ_COMP = "freq";
    protected org.apache.lucene.search.spell.SpellChecker spellChecker;
    protected String sourceLocation;
    /*
     * The Directory containing the Spell checking index
     * */
    protected Directory index;
    protected Dictionary dictionary;
    public static final int DEFAULT_SUGGESTION_COUNT = 5;
    protected String indexDir;
    protected float accuracy = 0.5f;
    public static final String FIELD = "field";
    protected StringDistance sd;

    @Override
    public String init(NamedList config, SolrCore core) {
        super.init(config, core);

        indexDir = (String) config.get(INDEX_DIR);
        String laccuracy = (String) config.get(ACCURACY);
        //If indexDir is relative then create index inside core.getDataDir()
        if (indexDir != null) {
            if (!new File(indexDir).isAbsolute()) {
                indexDir = core.getDataDir() + File.separator + indexDir;
            }
        }
        sourceLocation = (String) config.get(LOCATION);
        String compClass = (String) config.get(COMPARATOR_CLASS);
        Comparator<SuggestWord> comp;
        if (compClass != null) {
            if (compClass.equalsIgnoreCase(SCORE_COMP)) {
                comp = SuggestWordQueue.DEFAULT_COMPARATOR;
            }
            else if (compClass.equalsIgnoreCase(FREQ_COMP)) {
                comp = new SuggestWordFrequencyComparator();
            }
            else {//must be a FQCN
                comp = (Comparator<SuggestWord>) core.getResourceLoader().newInstance(compClass, Comparator.class);
            }
        }
        else {
            comp = SuggestWordQueue.DEFAULT_COMPARATOR;
        }

        String strDistanceName = (String) config.get(STRING_DISTANCE);
        if (strDistanceName != null) {
            sd = core.getResourceLoader().newInstance(strDistanceName, StringDistance.class);
            //TODO: Figure out how to configure options.  Where's Spring when you need it?  Or at least BeanUtils...
        }
        else {
            sd = new LevensteinDistance();
        }
        try {
            initIndex();
            spellChecker = new SpellChecker(index, sd, comp);
        }
        catch (IOException e) {
            throw new RuntimeException(e);
        }
        if (laccuracy != null) {
            try {
                this.accuracy = Float.parseFloat(laccuracy);
                spellChecker.setAccuracy(this.accuracy);
            }
            catch (NumberFormatException e) {
                throw new RuntimeException("Unparseable accuracy given for dictionary: " + name, e);
            }
        }
        return name;
    }

    @Override
    public SpellingResult getSuggestions(SpellingOptions options) throws IOException {

        SpellingResult result = new SpellingResult(options.tokens);
        IndexReader reader = determineReader(options.reader);
        Term term = field != null ? new Term(field, "") : null;
        float theAccuracy = (options.accuracy == Float.MIN_VALUE) ? spellChecker.getAccuracy() : options.accuracy;

        int count = Math.max(options.count, AbstractLuceneSpellChecker.DEFAULT_SUGGESTION_COUNT);
        for (Token token : options.tokens) {
            String tokenText = new String(token.buffer(), 0, token.length());
            term = new Term(field, tokenText);
            int docFreq = 0;
            if (reader != null) {
                docFreq = reader.docFreq(term);
            }
            String[] suggestions = spellChecker.suggestSimilar(tokenText,
                    ((options.alternativeTermCount == null || docFreq == 0) ? count
                    : options.alternativeTermCount), field != null ? reader : null, // workaround LUCENE-1295
                    field, options.suggestMode, theAccuracy);
            if (suggestions.length == 1 && suggestions[0].equals(tokenText)
                    && options.alternativeTermCount == null) {
                // These are spelled the same, continue on
                continue;
            }
            // If considering alternatives to "correctly-spelled" terms, then add the
            // original as a viable suggestion.
            if (options.alternativeTermCount != null && docFreq > 0) {
                boolean foundOriginal = false;
                String[] suggestionsWithOrig = new String[suggestions.length + 1];
                for (int i = 0; i < suggestions.length; i++) {
                    if (suggestions[i].equals(tokenText)) {
                        foundOriginal = true;
                        break;
                    }
                    suggestionsWithOrig[i + 1] = suggestions[i];
                }
                if (!foundOriginal) {
                    suggestionsWithOrig[0] = tokenText;
                    suggestions = suggestionsWithOrig;
                }
            }

            if (options.extendedResults == true && reader != null && field != null) {
                result.addFrequency(token, docFreq);
                int countLimit = Math.min(options.count, suggestions.length);
                if (countLimit > 0) {
                    for (int i = 0; i < countLimit; i++) {
                        term = new Term(field, suggestions[i]);
                        result.add(token, suggestions[i], reader.docFreq(term));
                    }
                } else {
                    List<String> suggList = Collections.emptyList();
                    result.add(token, suggList);
                }
            }
            else {
                if (suggestions.length > 0) {
                    List<String> suggList = Arrays.asList(suggestions);
                    if (suggestions.length > options.count) {
                        suggList = suggList.subList(0, options.count);
                    }
                    result.add(token, suggList);
                } else {
                    List<String> suggList = Collections.emptyList();
                    result.add(token, suggList);
                }
            }
        }
        return result;
    }

    protected IndexReader determineReader(IndexReader reader) {
        return reader;
    }

    @Override
    public void reload(SolrCore core, SolrIndexSearcher searcher) throws IOException {
        spellChecker.setSpellIndex(index);

    }

    /**
     * Initialize the {@link #index} variable based on the {@link #indexDir}.
     * Does not actually create the spelling index.
     *
     * @throws IOException If there is a low-level I/O error.
     */
    protected void initIndex() throws IOException {

        if (indexDir != null) {
            index = FSDirectory.open(new File(indexDir));
        }
        else {
            index = new RAMDirectory();
        }
    }

    /*
     * @return the Accuracy used for the Spellchecker
     * */
    @Override
    public float getAccuracy() {
        return accuracy;
    }

    /*
     * @return the Field used
     *
     * */
    public String getField() {
        return field;
    }

    /*
     *
     * @return the FieldType name.
     * */
    public String getFieldTypeName() {
        return fieldTypeName;
    }


    /*
     * @return the Index directory
     * */
    public String getIndexDir() {
        return indexDir;
    }

    /*
     * @return the location of the source
     * */
    public String getSourceLocation() {
        return sourceLocation;
    }

    @Override
    public StringDistance getStringDistance() {
        return sd;
    }

    public SpellChecker getSpellChecker() {
        return spellChecker;
    }
}
